Electrode



United States Patent Ofiice Patented Nov. 6, 1962 3,062,947 ELECTRODE John Campbell, South Plainfield, N.J., assignor to All Reduction Company, Incorporated, New York, N.Y., a corporation of New York No Drawing. Filed Nov. 5, 1959, Ser. No. 851,017 6 Claims. (Cl. 219-74) This invention relates to electric power are forming and sustaining apparatus and methods and more particularly to a non-consumable electrode and the operation thereof within a gaseous shield.

An object of the invention is to provide an arc-supporting electrode which is substantially non-consuming in an active shielding gas when subjected to the heat of an are maintained in said gas between said electrode and a cooperating electrode.

Another object of the invention is to provide a non consuming electrode operating as such when supporting a sustained heating are in an active gas at atmospheric pressures or above.

Another object of the invention is to reduce the cost of gas shielding a power arc, such as used in arc welding, arc cutting and like operations, by providing an electrode which will withstand operation in an atmosphere of chemically active gas.

A further object is to provide for ease in starting a power arc.

Arc systems comprising non-consuming or non-consumable electrodes have come into use as for are welding and cutting and in plasma torches. Heretofore, however, the non-consumable types of electrodes that have been available have been vulnerable to attack by atmospheric air and other chemically active gases. As a result the electrode was quickly contaminated or it disintegrated or both, so that it became necessary to shield the electrode with an enveloping stream of chemically inert gas during use in order that the electrode might have a useful life sufficiently long to be commercially feasible. Shielding gases are also used to provide a controlled atmosphere or expressly to exclude air and for these purposes also inert gases are commonly used. The inert gases commercially available are mainly argon and helium, which are relatively expensive. There is, therefore, a need for a less expensive system of power are operation with shielding gases. Since commercially available chemically active gases such as carbon dioxide, nitrogen and hydrogen are much cheaper than the inert gases, and since there are many instances in which it is desirable to operate the electrode in atmospheric air, an electrode which can be operated in air or within a shield of active gas meets the need for less expensive power are operation.

I have found that an electrode made of a boride of an element selected from the group of elements consisting of the rare earths is capable of resisting attack from chemically active gases in or surrounding a power arc. An electrode of lanthanum hexaboride has been found to be particularly efficient for use in supporting a power are in a chemically active atmosphere. Such electrodes may be made by cold compacting the boride in powder form and sintering the compacted mass in an electric vacuum furnace.

Electrodes of the type disclosed herein have been found to start an electric are very easily upon contact and separation from a work piece or another electrode, compared with electrodes now in general use.

The terms electric arc, heating arc and power are as used herein refer to a self-sustained high temperature discharge having a low voltage drop and capable of supporting large currents at atmospheric pressure or above.

Other objects, features and advantages of the invention will appear from the following more detailed description of illustrative embodiments thereof.

The electrodes of this invention may be made in any desired shape. For example, they may be in the form of rods about a quarter of an inch or more in diameter and of any desired length.

The electrodes may be used in various kinds of electric arc welding and heating apparatus, for example, in the arc welding apparatus disclosed and claimed in United States Patent No. 2,659,797, granted November 17, 1953 to N. B. Anderson and E. T. Sullivan and assigned to the same assignee as the present invention. In the apparatus of the above-cited patent, an electrode of the type described herein may be used in place of the tungsten or other non-consuming electrode 3 shown in the patent drawing.

The electrodes disclosed herein may also be used in plasma torches or other devices which use the heating effect of an are for fusing, cutting, severing or welding operations, for eifecting chemical or metallurgical operations or for any other operation employing an arc.

The shielding gas, however, used with the electrodes disclosed in the present application, need not be a chemically inert gas as used with the welding apparatus shown in Patent No. 2,659,797, but is preferably chosen from the active gases, for example, carbon dioxide, nitrogen, hydrogen, air, etc.

In order that the electrode shall not be consumed while in operation in an atmosphere of chemically active gas an electrode of such composition that it can withstand the action of the active gas must be used. I have found that an electrode suitable for this purpose can be made from certain borides. I prefer lanthanum hexaboride, LaB but other borides may also be used, for example, any of the borides of the rare earth elements. These materials are characterized by copious thermionic emission at operating temperatures, high melting points, and relatively great freedom from attack by the active gases.

Lanthanum hexaboride is preferred because it possesses a reasonably high melting point, known to exceed 2200 degrees centigrade, coupled with excellent thermionic emission characteristics. Lanthanum hexaboride in powder form, which will pass through a 40 mesh screen and has a stated purity of 97 to 98 percent is commercially available.

The electrode may be made from the boride by a method of powder metallurgy. The boride, for example, lanthanum hexaboride, in the form of a powder that will pass through a screen having 40 meshes to the inch, may be further pulverized as by milling in a tungsten carbide vibrating ball mill for about one-half hour. In a batch of 28 grams of powder that was used in making electrodes a sieve analysis after the pulverizing operation showed the following results:

Grams Passed by 40 mesh screen and stopped by 100 mesh 4.5 Passed by 100 mesh and stopped by 200 mesh 7.0 Passed by 200 mesh and stopped by 325 mesh 10.0 Passed by 325 mesh screen 6.5

From these screenings, a quantity of powder was compounded in the following proportions:

Parts Passed by 100 mesh and stopped by 200 mesh 5 Passed by 200 mesh and stopped by 325 mesh 3 Passed by 325 mesh screen 8 vacuum furnace. The furnace temperature was raised slowly at the start in order to minimize danger of breakage during the de-gassing stage of the sintering operation. A sintering temperature was then maintained for about one-half hour.

The pressure in the cold compacting operation may be 50 tons per square inch. The sintering may be done at a temperature of 1300 degrees centigrade to 1800 degrees centigrade. The product made at 1300 degrees is machinable while the product made at 1800 degrees is too hard to be machined.

The grain sizes in the powder mixture may be varied in order to establish by experiment a mixture which results in a maximum density in the finished product. The density may be 3 grams per cubic centimeter or higher, and preferably at least 3.7 grams per cubic centimeter.

A test was made using an electrode of lanthanum hexaboride and a steel workpiece in a shielding atmosphere of carbon dioxide. An arc was easily established by touching the electrode to the workpiece and withdrawing it therefrom. The are voltage was found to be 35 volts and the are operated in stable manner over an indefinitely long period of time. No perceptible attack upon the electrode by the carbon dioxide was found. Using nitrogen as the shielding gas, the arc voltage was found to be 28 volts. The effect of the nitrogen upon the electrode was found to be very slight and not detrimental in any way to the operation of the arc. When the electrode was operated in atmospheric air, the arc voltage was found to be 30 volts and the effect of the air upon the electrode was found to be similar to the effect of nitrogen. The electrode was also found to operate in an entirely satisfactory manner in the inert gases, argon and helium.

A shielding atmosphere of carbon dioxide is found to be particularly desirable in welding steel, especially for low alloy steels. For welding copper, a nitrogen shield is suitable. Nitrogen is also appropriate for use in cutting or severing operations using a power arc. In general, any chemically active gas may be used as a shield in conjunction with the type of electrode herein disclosed, the choice of gas being limited only by the reaction of the gas upon the workpiece.

The are may be drawn either between an electrode and a workpiece or between two electrodes.

The relative polarity of the electrode and the workpiece is not important in the system herein disclosed and either direct current welding or alternating current welding may be practiced therewith.

While illustrative forms of apparatus and methods in accordance with the invention have been described herein, together with a method for manufacturing electrodes, it will be understood that numerous changes may be made without departing from the general principles and scope of the invention.

What I claim is:

1. A non-consuming electrode operating as such when supporting a sustained heating are in an active gas at atmospheric pressures or above, said electrode consisting of a hexaboride of a single rare earth element.

2. A non-consuming electrode operating as such when supporting a sustained heating are in an active gas at atmospheric pressures and above, said electrode consisting of briquetted, sintered lanthanum hexaboride having a density greater than 3 grams per cubic centimeter.

3. A non-consumable electrode for electric arc welding and cutting in an atmosphere comprising a gas selected from the group consisting of carbon dioxide, nitrogen, hydrogen and air, said electrode comprising essentially a rare earth metal boride.

4. A non-consumable electrode according to claim 3 in which the rare earth metal boride is selected from the group consisting of lanthanum hexaboride, and cerium hexaboride.

5. A non-consumable electrode for carbon dioxide shielded arc welding and cutting comprising a sintered body consisting essentially of lanthanum hexaboride.

6. A method of electric arc welding 21 ferrous metal workpiece which comprises striking an are between said ferrous metal workpiece and a non-consumable electrode of a rare earth metal boride, and shielding the are end of said electrode, said arc, and the weld puddle formed on said workpiece with a flowing stream of carbon dioxide.

References Cited in the file of this patent UNITED STATES PATENTS Reed et al. Feb. 17, 1959 Nestor Sept. 29, 1959 OTHER REFERENCES 

1. A NON-CONSUMING ELECTRODE OPERATING AS SUCH WHEN SUPPORTING A SUSTAINED HEATING ARC IN AN ACTIVE GAS AT ATMOSPHERIC PRESSURES OF ABOVE, SAID ELECTRODE CONSISTING OF A HEXABORIDE OF A SINGLE RARE EARTH ELEMENT. 